Catalytic distillation technology is a recently developed chemical engineering process, which combines catalytic step with distillation step, so that reactions and separations are carried out in the same column simultaneously. The process is capable of removing reaction products from each reaction-separation unit continuously and making use of reaction heat as the vaporization heat required for carrying out distillation. The catalytic distillation technology is characterized by higher conversions, better selectivity, less energy consumption, higher product purity, more convenient operation and less investments and so on, which has been widely researched and rapidly developed since the 80's. Such a technology first succeeded in the application for producing methyl t-butyl ether (MTBE) and then become widely used in many other areas.
A key to the catalytic distillation technology lies in the method by which the catalysts are filled into the reaction sections. Catalysts are filled in many ways which are generally divided into two types: one is a separate way, and the other is an integrated way. The process of the separate way produces catalysts and distillation packings separately, that is, catalysts are directly manufactured into granulates of various shapes and sizes, then combined with distillation packings by various means, and finally filled into distillation columns. For example, as described in U.S. Pat. No. 4,443,559 catalysts granules are filled in bulk into textile bags and supported by a stainless steel wired mesh covering having certain openings, which are rolled into cylindrical rolls consisting alternately of wired mesh layer and fabric bag's layer and form composite materials for use in distillation columns. According to another method of filling catalysts with packings in bulk disclosed in U.S. Pat. No. 5,262,012, granular catalysts are mixed with inert filling media such as ceramic balls, glass beads, hollow and porous balls or cylinders and then filled into columns. The major deficiency of the separate filling form lies in unevenly distributed catalysts in the bed, an excessive local pressure drop, poor gas/liquid flow, resulting in a non-uniform mixing, a non-uniform distribution in concentrations, and even undesirable dead corners. Moreover, design and fabrication of the composite are complex, the technical requirements are rigid, and filling and removal of packings are inconvenient, which are unfavorable to its application in the industry.
The process of integrated type combines catalysts and distillation packings as a whole to form an unitary and uniform element, and then put the element into a catalytic distillation column. For example, CN 1060228 describes a catalytic reaction-rectification column, wherein both trays or plates or packings in the column are directly formed by using active materials containing catalysts, which resolves problems of packing and filling of catalysts for catalytic rectification columns; however, the direct use of a catalytic active substances in forming the trays and packings leads to poor stength thereof, and further, elevated temperature and other factors during the production of trays and packings resulte in reduction or even lose of catalytic activity. In addition, the costs of both the trays and the packings are relatively higher.
Take futher examples, CN 1167009 discloses a mordenite/metal ceramic composite, which is prepared by incorporating an uniform layer of mordenite molecular sieve directly onto the surface of a metallic or ceramic substrate which is designed in advance and has an arbitrarily selected shape and size. CN 1228032 describes a catalytic packing useful in catalytic distillation process, which is prepared by vapor-depositing and/or spraying at least one active material as catalysts and/or promoters onto a substrate such as textiles, knitting or sheet-like packings. U.S. Pat. No. 5,235,102 discloses a catalytic distillation process for converting a feed stream in gas or liquid phase into desired products; one of the embodiment uses a rigid honeycomb ceramic block coated with catalytic active components as packings in a catalytic distillation column. In all the disclosed processes mentioned above, there always exist the problems: no matter on what a susbtrate, e.g. metals, ceramics, or textiles, the catalytic active coatings prepared by impregnation in liquids, vapor-depositing or spraying methods exhibit poor adhesion strength, which may peel off or be destructed, and thus damag the performances of catalysts. Accordingly, there still remains an urgent needs to improve the adhesion strength between a substrate and an active component layer.